Payment Methods: add PayPal as option to PaymentMethodForm

[michaeldcain]

In #47516, we're creating a new PaymentMethodForm component for the "Change Payment Method" (EditCreditCardDetails) screen. After we create the new endpoints to create and save PayPal billing agreements (tracked separately), we'll want to add PayPal as an option to this form.

See: pbOQVh-Dt-p2

User Flow:

• user selects "Add {a|another} PayPal account" from radio options on "Change Payment Method"
• user click "Continue"
• user is redirected to PayPal site
• user confirms new billing agreement
• user is returns to Subscription Settings screen with confirmation(?) and payment method is updated on setting screen